Any time I've had to do NDA's, I've always run it past my attorney, but then I've always had a working model before seeing NDA's, so maybe that was what the protection was on (rather than the idea).

You can't copyright the idea as in "I want to build a site", but if you document a highly detailed design plan, flow charts and other documents for example, you could copyright that information.

(in England) the moment the idea takes a tangable form in any way, you can protect it - http://www.ipo.gov.uk/

It seems things get a little reversed between the US laws and UK laws. I'll have to do some digging for US pattent and copyrights - but the moment the idea takes form, it can be and shoudl be protected (from what I've read)